塔里木盆地致密砂岩气储层微观孔隙结构

Microscopic pore structure for tight sandstone gas reservoirs in Tarim Basin

为研究塔里木盆地库车坳陷储层储集条件及其微观孔隙结构,应用核磁共振技术测定不规则岩样核磁孔隙度与核磁渗透率,应用高速离心实验标定岩样T2截止值,划定可动流体饱和度与不同喉道半径控制的可动流体体积分数,应用低温氮气吸附实验,深入分析岩样微观孔隙结构,建立致密砂岩储层渗透率、可动流体饱和度与微观孔隙特征之间的关系。研究结果表明：库车坳陷J1a层位致密砂岩气藏在深度4-5 km的储层占主要部分,平均渗透率0.021×10^-3-3.982×10^-3μm^2,平均孔隙度2.96%-7.17%;平均比表面1.83-2.35 m^2/g,为页岩的1/10;该储层中半径为50 nm以下喉道控制孔隙占总孔隙60%左右,半径50 nm以下孔隙以介孔为主,平均占总孔隙的33.03%。当渗透率由0.1×10^-3μm^2以下逐渐增大至1×10^-3μm^2以上时,砂岩孔隙形状由墨水瓶孔为主逐渐变为平行板状孔,再逐渐变为V型孔。库车坳陷致密砂岩气物性较差,占总孔隙27%的由半径50 nm以下喉道控制的较大孔隙可以作为致密砂岩气藏进一步开发突破点。

In order to investigate the reservoir conditions and microscopic pore structure in the Kuqa Depression, Tarim Basin, the NMR porosity and permeability were analyzed by using the nuclear magnetic resonance technology for the irregular rock sample. T2 cutoff of the rock sample was calibrated and the movable fluid saturation and movable fluid percentage controlled by different throat radius were delimited by using the centrifugal experiment method. Simultaneously, the cryogenic nitrogen adsorption was applied to analyze the microscopic pore structure, and the relations between the tight sandstone reservoir permeability characteristics, the movable fluid saturation and microscopic pores were established. The results show that the Kuqa depression J1 a layers of tight sandstone gas reservoirs in 4-5 km depth accounts for the major part, the average permeability is 0.021×10^-3-3.982×10^-3 μm^2, the average porosity is 2.96%-7.17%, and the average surface area is 1.83-2.35 m2/g, which is 1/10 of the shale. The pore is controlled by throats whose radius is less than 50 nm, which accounts for about 60% of total pore. The pore whose radius is below 50 nm accounts for about 33% of the total porosity. When the permeability increases from less than 0.1×10^-3 μm^2 to more than 1×10^-3 μm^2, the sandstone pore shape dominated by the inkbottle-like pores gradually becomes parallel plate hole, and then gradually becomes V-shaped hole. Overall tight sandstone reservoirs properties are relatively poor. The large pores, about 27% of the total pore, are controlled by the throats below 50 nm, which can serve as a breaking point for development of tight sandstone gas reservoirs.